1. FIELD OF THE INVENTION
This invention relates to a mechanical seal for use in a rotary machine for generally handling fluid under pressure such as a pump and a compressor.
2. DESCRIPTION OF THE PRIOR ART
In a machine for circulating fluid under pressure, a mechanical seal is used whereby leakage from a high pressure region to a low pressure region along a rotary shaft is prevented. Along with the advance in techniques, the machines using the mechanical seals of the type described are operated under the severe conditions such as high temperature, high pressure and high speed. Hence, recently, it is particularly required of a mechanical seal to display stable sealing performance even under said severe conditions such as high temperature, high pressure and high speed. With the purposes of maintaining the temperature of the mechanical seal within the suitable range and preventing impurities from accumulating in a shaft sealing portion to thereby meet the above requirements, such measures have been taken that flushing method for feeding fluid to or feeding to and discharging from the shaft sealing portion is improved, or grooves are provided in the sliding seal surface of the sealing elements whereby fluid is forcedly introduced into the sliding seal surface by utilizing the rotation of the sliding seal surface to thereby increase pressure of a fluid film of the sliding seal surface. However, even if said measures are taken, such problems cannot be obviated to the full extent that the volume of leakage is extremely increased, or rapid cooling or heatgenerating is alternately repeated, thus creating heat cracks at the sliding seal surface, and further the sliding seal surface becomes rough due to high temperature, thus resulting in unduly high wear and unduly leakage. Despite the circumstances described above, the requirements on sealing required of the sealing device have been becoming severer at a rapid rate at present.